Co-owned U.S. Pat. No. 6, 035,828 to Anderson et al. describes a hydraulically actuated system having a variable delivery fixed displacement axial piston pump. This pump is referred to as a fixed displacement because the swash or drive plate has a fixed angle such that each piston reciprocates a fixed distance and displaces a fixed amount of fluid with each rotation of the drive plate. The pump achieves a variable delivery by utilizing sleeves that surround each piston and cover a spill port for at least a portion of each reciprocation of the individual piston. For instance, if the sleeves are positioned at one location, the spill ports in the pistons remain uncovered throughout each reciprocation such that the pump merely circulates fluid between low pressure areas and no high pressure output is produced. When the sleeves are in another position, the spill ports are closed over the entire reciprocation distance of the piston such that the maximum high pressure output of the pump is achieved. The sleeves can be positioned anywhere between these two extremes via an electro-hydraulic control unit so that the effective high pressure delivery of the pump can be varied and controlled at will.
While this pump has shown considerable promise, there remains room for improvement. For instance, each of the pistons has one end received in a piston bore of a barrel component. A high pressure collection cavity is located between the barrel and the outlet of the pump. In addition, at least one check valve separates the individual piston chambers from the high pressure collection cavity. In the Anderson et al. pump, these various features are located in body components that are different from the barrel. As such, the effectiveness of the pump has the potential for compromise due to leakage between these components. In addition, insuring the proper location and orientation of these body components relative to one another can add substantial machining costs and assembly complications.
The present invention is directed to one or more of the problems set forth above.